Detecting Prominences from Century-long Disc-blocked C\MakeLowercase{a}~{\sc ii}~K Spectroheliograms of Kodaikanal Observatory

Abstract

Kodaikanal Solar Observatory (KoSO) has recently digitised the long-term (1906-2002) disc-blocked Ca~{\sc ii}~K spectroheliograms. This data has been archived at \url{https://kso.iiap.res.in}. The intriguing features seen in the images are the off-limb prominences which provides a proxy for understanding the solar magnetic activities over a long period of time. To make use of this unique dataset we performed calibration of the raw data and developed an automated technique to identify the prominence locations on daily images. We use the recorded prominence latitudes to generate their time-latitude distribution and find clear signature of poleward migration for about 8 cycles complementing the H\(_\alpha\) observation in KoSO. We study the drift rate of polar prominences across solar cycles and latitudes. North-South asymmetries of the drift rates are also computed. We show how latitudinal distribution of prominences vary over a period of 11 years and the dominant latitudes in the aggregate distribution. As one of major sources of coronal mass ejection (CME) is eruptive prominence, the latitudinal distribution of prominences can provide additional input for the understanding of the generation of CMEs, particularly the slow CMEs. Clear depiction of polar rush for multiple cycles presented in this work should be valuable in the study of prediction of solar cycles.